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Model C-15 Rosewood & Western Redcedar

Cozad C-15 Binding

Specifications:

  • Body Style: C-15
  • Upper Bout: 11.25″
  • Waist: 9″
  • Lower Bout: 15″
  • Body Length: 19.5″
  • Body Depth (Tail block): 4.625″
  • Scale Length: 25.4″
  • Soundboard: Western Redcedar
  • Back and Sides: East Indian Rosewood
  • Bracing: Adirondack Red Spruce
  • Bracing pattern: Back - Conventional ladder, Soundboard - Double-X
  • Binding: Gabon Ebony
  • Soundhole Binding: Indian Rosewood
  • Rosette: Paua
  • Neck: 5-piece Mahogany
  • Fingerboard: Gabon Ebony
  • Fingerboard Inlay: Mahogany and Paua
  • Headplate: Gabon Ebony
  • Bridge: Gabon Ebony
  • End graft: Gabon Ebony
  • Options: Soundboard Inlay

There was a time when trees, large enough in diameter to fashion a large guitar’s soundboard or back entirely from a single slab or billet of wood, were in plentiful supply. Within the last century, as large trees were harvested faster than they were re-planted, the option of beginning with a single, massive plate of wood began to quickly disappear. Regardless of availability, the potential for splits across that large of a span of wood due to seasonal or environmental movement could be mitigated by ripping large plates lengthwise and rejoining them, improving their stability.

Book matching, the practice of slicing two (2) adjacent plates (from the same half of the tree), laying them open like a book, and joining them opposite a center seam (creating a mirror image of the grain pattern) proved to be more structurally sound, more popular and more aesthetically pleasing than looking at a single, large cross-section of a tree.

I use a plate joiner jig to glue two (2) book matched halves of the Cedar soundboard of this deep-bodied, OM-sized guitar together. The two (2) book matched halves that make up the Rosewood back are assembled in the same manner. For both front and back plates, two (2) boards are matched, planed (thicknessed/thinned), glued and assembled into this clever contraption which pulls them tightly together with very even pressure while preventing them from buckling as the glue dries.

Cozad C-15 Plate Joiner
Plate joiner

The 30 year-old Cedar (the tree was several hundred years old! It had been 30 years since the book matched pieces had been cut) I used for the soundboard is among the stiffest I have ever encountered. Cedar, while exceptionally stiff across the grain, tends to be weaker along the grain than Spruce. As a result, Cedar Soundboards are typically a bit thicker than their Spruce counterparts. But not this one! I have high hopes for this guitar!

I route the purfling and Paua soundhole rings using a rotary tool mounted in a mini router jig and attached to a circle cutter. After the inlay work is complete I cut a circle all the way through the soundboard, creating the soundhole.

This opening allows air to pump in and out of the enclosed chamber that comprises the body of the acoustic guitar. That pumping action is initiated by the vibration of the steel strings which, on this guitar, will be exerting upwards of 160 lbs. of tension at the bridge. The kinetic energy produced by the vibrating strings transfers across the saddle, down into the the bridge/bridgeplate assembly, and radiates across the soundboard in waves, very much like water in a small pool. In reaction, the soundboard moves (or flexes) up and down similar to a speaker cone resulting in what we refer to as both the “sound” and “tone” of the guitar.

Cozad C-15 Soundboard
Soundboard

A close-up image highlights the beauty of the combination of Cedar, Paua, and black-white-black (BWB) purfling circling the soundhole, forming a series of decorative concentric rings that are often referred to collectively as a rosette.

Cozad C-15 Soundhole
Soundhole

When the stiffness and thickness of the soundboard are considered, the bracing (material, pattern, dimension) is adjusted accordingly. For this particular instrument, I chose to employ a progressive double-X bracing pattern with a Rosewood bridgeplate. I wanted to coax the brightness out of this top, and I have found the double-X pattern to be very suitable for the task. To maximize volume, I will keep the soundboard at a relatively flat 50° (the additional “X” of the below the bridge will add the extra support where it’s needed, especially for this flat of a top).

Near the center of the lower bout of the soundboard, directly beneath the bridge, lies the bridgeplate. There has been speculation that this thin piece of material (traditionally, Rosewood or Maple) became popular among luthiers during the advent of the ball-end strings, as the steel ball would quickly chew through the softwoods used for the soundboards. Another significant function of this plate, which effectually sandwiches the soundboard between bridgeplate and bridge, is to prevent the bridge from simply peeling off the soundboard as a result of string tension by assisting in keeping the soundboard flat(ter). It just so happened I had several Rosewood plates already cut to size.

Undersized or overly-thin bridgeplates can accompany guitars having the most impressively low frequency response (lots of bass)...albeit short-lived, as the soundboards will often begin to pull, or belly, upwards. That is not necessarily a problem, tone-wise, but it does present a major challenge in estimating the (eventual) neck angle. The angle at which the plane of the fingerboard encounters the (approximate) plane of the contoured/radiused soundboard must be optimized to prevent the strings from either lying on the frets or standing too far off the frets. Guitars that belly (pull upward due to string tension) significantly typically end up requiring early neck resets, as the strings eventually rise too high above the fingerboard for comfortable playing, and no amount of saddle height adjustment can correct the problem.

Rapid bellying after initial construction is evidence of insufficient soundboard stiffness / bracing strength / bridgeplate size.

Conversely, too large a bridgeplate is a real tone killer (as is too thick or too stiff a soundboard, along with too much bracing). Sizing a bridgeplate incorrectly can critically impact the performance of the instrument.

While arguably sacrificing some lower frequency response, leaning slightly toward a larger plate versus a smaller plate provides the peace of mind that the soundboard will stay where it belongs over time.

The soundhole is bound in Rosewood and a carbon fiber fingerboard patch is epoxied across the soundboard next to the transverse brace. On most steel string acoustics, the fingerboard extension (the part of the fingerboard that extends out onto the soundboard, toward the soundhole, past the point where the neck meets the body) is glued directly to the soundboard. The two (2) materials expand and contract at different rates. A fingerboard patch is applied to the backside of the soundboard to minimize the soundboard’s contraction and expansion at this critical juncture. In the case of this guitar, the fingerboard extension is not glued but rather secured to the soundboard using a small nylon bolt. The epoxied carbon fiber provides something more significant than soft Cedar to attach the fingerboard to.

Cozad C-15 Double X Brace
Double X-brace

The soundhole reinforcement is added, it’s purpose here is to provide protection for the thin Cedar soundboard. Here, unused Rosewood material from the side of the guitar is re-purposed.

Cozad C-15 Soundhole Reinforcement
Soundhole reinforcement

Note this particular bracing profile’s similarity to duck heads or bottlenose dolphins. These braces are glued onto the soundboard as long, thin interlocking rectangles, and are both scalloped and shaped in place with a chisel. Some careful sanding dresses them up for final presentation. The objective is to support significant string tension while allowing the soundboard to vibrate as freely as possible from the plucked strings energy. It is a delicate balance: An over-braced soundboard results in a rather dull, lifeless guitar, as the strings must be strummed or plucked hard in order to generate any front plate vibration which, in turn, is dampened by all that bracing. An under-braced soundboard can result in a collapse or implosion, though it will likely sound wonderful during it’s short life.

The goal is to brace the soundboard just enough to prevent it from collapsing over time, and never so much as to dampen it’s sonic potential.

Cozad C-15 Soundboard Bracing
Soundboard bracing

The Basswood reverse kerfing is applied to the top and bottom of the Rosewood sides (destined to support the front and back of the guitar, respectively), extending from neck block to tail block. This lightweight ledge / rim supports the front and back plates, providing a more substantial glue surface at the sides.

Cozad C-15 Rosewood Sides in Body Mold
Rosewood sides in the body mold

Braces are added to the Rosewood back. A center graft is intentionally omitted.

With the advent of modern glue(s) and proper clamping, back plate center grafts serve little purpose but to add weight.

Cozad C-15 Back Braces
Back braces

The back is joined to the sides (one simply cannot have too many clamps, can one?).

Cozad C-15 Glueing On Back
Glueing on the back

A view of the tail block shows a recess for the drilling of a (completely optional) through hole. This hole will receive an end pin jack, as electronics will be added, later. It could get a traditional end pin, just as easily.

Cozad C-15 Tail block
Tail block

This view of the neck block shows the two (2) recessed holes for the bolts used to secure the neck to the body. Much has been written and discussed regarding the particular method of attaching the neck to the body, with camps dividing over the traditional glued-in dovetail and bolted-on mortise and tenon. This guitar will be made using the bolt-on neck approach. I cannot measure any tone loss between the two methods and neck adjustments (neck resets) are dramatically easier to perform! If there is a downside to a bolt-on neck, it would be the additional weight of the metal hardware.

Cozad C-15 Neck block
Neck block

All four (4) braces on the back plate and the primary X brace and transverse brace on the front plate are deliberately left longer than the dimensions of the body. The sides will be notched to receive these through braces, allowing the ends of these braces to rest directly on the sides while the balance of the front (and back) rests upon the kerfing.

Cozad C-15 Notched For Braces
Notched for braces

The guitar’s sides (sometimes referred to as “ribs”) are also reinforced, albeit with very small, lightweight braces.

Cozad C-15 Notched For Braces
Side braces

The soundboard (front plate) is glued on.

Cozad C-15 Gluing On Soundboard
Glueing on the soundboard

A decorative plate known as an end graft is added to the end of the guitar, spanning what would be the seam formed by the two (2) sides butting together at the tail block. This wooden wedge provides for a visually pleasing break in the seams of the guitar sides as well as eliminating the need to perfectly align and match the grain of the two (2) sides. Even when sides are matched correctly, without an end graft it often looks like something is missing or was forgotten.

Aggravatingly, a dark grain line displays prominently just 1/32″ off center, where the two (2) halves of the front plate join. I hadn’t noticed it until it was compared with true center, as you see in these two (2) photos of the end graft. Argh!

Cozad C-15 End Graft Routed
End graft routed

But the end graft looks so good it makes me feel better! ;~}.

Cozad C-15 End Graft Routed Applied
End graft applied

Rabbets are routed along the front and back and Ebony binding (or binding with additional purfling) is glued on. Binding serves more than one purpose: It is primarily understood to be intended to buffer bumping the instrument into furnishings and the like, considering that the soundboard is most often made from a softwood. However, I have found this to be a side benefit compared to the function of it’s mimicking the side wall of the swimming pool, reflecting some of the sound waves that ripple away from the bridge back across the soundboard. For a dramatic demonstration of this “reflection” effect, route off the binding from an existing guitar and listen to the difference! An additional benefit is the aesthetically pleasing visual transition between the front or back plates and the sides.

The neck is cut on a bandsaw. Here I have cut two (2) necks from a laminated block of Mahogany (My neck blanks are resawn, planed and glued back together with additional wood strips for the purpose of increasing stability and adding visual interest to the back of the neck).

The neck is intentionally cut wider and thicker than it’s final dimensions, as it will be sized and shaped to final dimensions in a later step.

Cozad C-15 Neck Blanks
Neck blanks

Not everyone feels the need to embellish the shape of their headstock, but I do. A distinct shape can be readily identified with the builder, and provides an opportunity to be creative. I worked diligently to produce a unique, yet simple design, one that both honored the instruments that inspired my efforts and let be make my own statement.

Cozad C-15 Headstock Outline
Headstock outline

Here we see the two (2) most basic components of an acoustic guitar, the neck and the body.

Cozad C-15 Neck and Body
Neck and body

An Ebony fingerboard will be glued to the neck. In addition to being perfectly flat, the fingerboard must be slotted to hold metal frets that have been carefully spaced using a template and a table saw jig. I use a steel fret slotting template in conjunction with a dedicated crosscut sled for accuracy and repeatability.

Cozad C-15 Fret Slotting
Fret slotting

This fingerboard will receive some decorative inlay. I have sketched an idea on paper.

Cozad C-15 Fingerboard Inlay Sketch
Fingerboard inlay sketch

I transfer the drawing to wood and cut out the shapes by hand. The vine is fashioned from a single piece of mahogany using a jeweler’s saw.

Cozad C-15 Fingerboard Inlay Cutting
Fingerboard inlay cutting

Many people are intimidated by the perceived degree of difficulty of this type of work. In no way do I mean to under-value the art form of inlay when I say that it is tedious, but it is not difficult. Attention to detail, patience and a steady hand are required.

Cozad C-15 Fingerboard Inlay Cut Out
Fingerboard inlay cut out

The fingerboard is mounted to a clever jig that is passed through a drum sander several times, rotating the fingerboard along it’s length on each pass. This results in an ever-so-slightly convex (radiused) surface that is then finished by hand. After radiusing, the fingerboard is routed to receive the inlay.

Cozad C-15 Routing for Inlay
Routing for inlay

Several small florets are cut from Paua and inlayed into the fingerboard along with the mahogany vine. The placement of the florets is not accidental, but instead provides the player with a quick visual reference for finger placement.

The inlay is added after radiusing the fretboard, in order to minimize any sanding of the material (if it was inlayed while the fingerboard was flat, and then the fingerboard was radiused, that extra sanding could sand right through the inlay material).

Cozad C-15 Fingerboard Inlay Complete
Fingerboard inlay complete

More mahogany vine and Paua florets are cut and set aside for inlaying the soundboard. The vine will appear to curl off the fingerboard and onto the upper bout of the body.

Cozad C-15 Fingerboard Inlay Complete
Body Inlay

The neck gets stiffened using two (2) carbon fiber rods. I believe the extra stiffening is beneficial. It adds torsional stability, is (potentially) lighter than the wood it replaces, and results in a "brighter" neck (replace the neck material with sound-dampening rubber and note the difference).

Cozad C-15 Carbon Fiber Stiffeners
Carbon fiber stiffeners

A close-up of the carbon fiber rods, epoxied into the neck.

Cozad C-15 Carbon Fiber Closeup
Carbon fiber closeup

The slot for the two (2)-way, adjustable truss rod is routed. Note that the adjustment occurs through the soundhole, leaving the wood at the headstock as thick as possible. This, combined with the carbon fiber rods, strengthens an otherwise structurally weak area of an acoustic guitar. I have never had a neck break at this location, though I have never deliberately attempted to break one, either.

Cozad C-15 Truss Rod Slot
Truss rod slot

A close-up of the truss rod slot.

Cozad C-15 Truss Rod Slot Closeup
Truss rod slot closeup

A mortise is cut into the body of the guitar using a plunge router. A router jig and template, called an edge vise, is used for exact positioning. This tool is used in conjunction with a precision neck angle jig.

Cozad C-15 Mortise Template
Mortise template

This jig acts as a second pair of hands and is fashioned to support the guitar securely, yet do no damage.

Cozad C-15 Body Jig
Body jig

A close-up of the mortise cut into the body.

Cozad C-15 Mortise
Mortise

This neck is held to the body using two (2) socket head cap screws, wavy washers and steel cross dowels (threaded inserts may be used in place of cross dowels, and are lighter in weight).

Cozad C-15 Neck Bolts
Neck bolts

Holes are drilled in the neck, prior to cutting the tenon, in order to house the cross dowels.

Cozad C-15 Cross Dowel Holes
Cross dowel holes

The neck is then clamped into the neck angle jig where the tenon is cut using the same plunge router that cut the mortise. The angles of the cuts are very important.

Cozad C-15 Tenon
Tenon

The neck, with tenon cut, and the body, with mortise cut...

Cozad C-15 Neck and Body
Neck and body

First fit (it is looking more and more like a real guitar!). The tenon fits tightly into the mortise, and the bolts secure the neck in place, snug up against the body.

Cozad C-15 First Neck Fitting
First neck fitting

Decorative purfling is added to the sides and back. Much like fingerboard inlay, the work is tedious but not difficult. And the results speak for themselves - very dressy!

Cozad C-15 Side Purfling
Side purfling
Cozad C-15 Back Purfling
Back purfling

With the truss rod secured in the slot, the fingerboard is aligned and glued to the neck. The neck is shaped and dimensioned using nothing but hand tools. A coarse rasp does the rough shaping, a file shapes the curves, and a spokeshave smoothes the straight lines.

Cozad C-15 SNeck with Fingerboard (Headstock)
Neck with fingerboard (Headstock)
Cozad C-15 Neck with Fingerboard (Heel)
Neck with fingerboard (Heel)

The fingerboard is drilled and tapped at the 19th fret, and a pair of nylon bolts are epoxied into place. This provides a means of securing the fingerboard to the face of the guitar that is light in weight and can easily be detached.

Cozad C-15 Fingerboard with Nylon Bolts
Fingerboard with nylon bolts

Here is a view from inside the box. The neck has been attached using the socket head cap screws, and the fingerboard extension is held tight to the soundboard with the help of nylon bolts and wingnuts. Note that the bolts pass through the carbon fiber fingerboard patch, which serves double-duty by providing an extra layer of support.

Cozad C-15 Detachable Neck
Detachable neck

The headplate is glued on to the headstock and shaped to follow the existing contours.

Another trip to the bench with the jeweler’s saw, and my spiral “C” (for Cozad) logo is cut from Paua shell, traced onto the headstock and inlayed. When creating my logo, I deliberately shaped this letter to present an optical illusion of a spiral when viewed in the context of the shape of the headstock.

While it is much easier (and less stressful) to inlay a headplate before it is glued to the headstock, the challenge of perfectly locating a finished headplate during glue-up soon overcomes the extra care needed to inlay it after it is glued in place.

Cozad C-15 Paua Logo
Paua logo

The headstock is drilled to accept the tuners. These are Gotoh SGV510Z chrome tuning machine heads with black BL5 buttons and a silky-smooth 21:1 gear ratio. A shallow recess, slightly larger than the tuner washers, is also drilled to house the washers and nuts.

NOTE: This is an aesthetic enhancement I have learned from Kent Everett, a look that I really like. Typically, machine head washers and nuts sit atop the headplate. Slightly insetting the washer and nut adds a distinctive visual element.

Cozad C-15 Machine Heads
Tuning machine heads

When I was moving the body of the guitar in preparation for finishing, I {cringe} made a small dent in the cedar top. I paused to determine whether to attempt to steam out the dent or to proceed with an alternate plan to decorate the soundboard. I chose to add the additional inlay to the upper bout of the soundboard, incorporating the area of the dent (and I was extra careful not to make any new dents).

The body gets inlaid with extra vine.

Cozad C-15 Body Inlay
Body inlay

The bridge is fashioned from a piece of Ebony (coordinated to match the fingerboard, headplate and end graft). Measurements are calculated and the soundboard is lightly marked where the bridge will be glued.

Cozad C-15 Ebony Bridge
Ebony bridge

The bridge is temporarily bolted to the soundboard and strings are added...

When using a bridge pin styled bridge, the bridge can be temporarily secured to the soundboard using a clever tool called an acoustic bridge bolt in two (2) of the six holes that have been drilled to accept the bridge pins. The brass bolts are center-drilled through their length, allowing guitar strings to be passed through the hollow centers. Using these bolts to hold the bridge on the soundboard, the guitar can be strung up for a sound test prior to finishing. Note that there is very little, if anything, that can be done about it at this point if you don’t like what you hear, but it is a clever way to sample what is coming!

This guitar just happens to sound amazing! I knew that Redcedar top was going to be special. Keeping the top on the flat side gave it outstanding volume. It is delightfully bright for a Cedar-topped guitar, thanks to the bracing design.

Cozad C-15 Ebony Bridge and Strings
Ebony bridge and strings

With the neck secured to the guitar the fret wires are cut, inserted into the fretboard, leveled, crowned and polished.

Cozad C-15 Fret Job
Fret job

Are you interested in learning more about this guitar? or would you like to inquire about a custom made Cozad guitar?

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